System and method for locating a disturbance in a power system based upon disturbance power and energy

ABSTRACT

A disturbance locating system deployed within a power grid to estimate a location of a disturbance in a power system includes a voltage transducer, a current transducer and disturbance energy determination circuitry. The system may also include disturbance power determination circuitry. The voltage transducer couples to an output of a voltage transformer, the output of the voltage transformer representative of a voltage on a line within the power grid. The current transducer couples to an output of a current transformer, the output of the current transformer representative of the current flowing through the line, the output having a forward reference direction and a behind reference direction. The voltage and current transformers may be hard wired to the line. The disturbance energy determination circuitry couples to the voltage transducer and the current transducer. Based upon the inputs received, the disturbance energy determination circuitry determines disturbance energy flowing in the line and estimates a direction of disturbance energy flow with respect to the system as either in front of or behind of the disturbance locating system. The disturbance energy determination circuitry may include disturbance power determination circuitry that couples to the voltage transducer and the current transducer. In such case, the disturbance power is provided to the disturbance energy determination circuitry for estimating a relative direction to the disturbance.

CROSS-REFERENCE TO A PROVISIONAL APPLICATION

This application is a continuation application under 35 U.S.C. § 120 andclaims priority from, and hereby incorporates by reference for allpurposes, copending U.S. patent application Ser. No. 09/207,969,entitled System and Method for Locating a Disturbance in a Power SystemBased Upon Disturbance Power and Energy, naming Parsons et al. asinventors, filed Dec. 9, 1998 now U.S. Pat No. 6,360,178, which,pursuant to 35 U.S.C. § 119(e), claims the benefit of U.S. provisionalPatent Application Ser. No. 60/069,164, entitled System and Method forLocating a Disturbance in a Power System Based Upon Disturbance Powerand Energy, naming Parsons et al. as inventors, filed Dec. 9, 1997.

BACKGROUND

1. Technical Field

The present invention relates generally to power systems; and moreparticularly to a system and method of operation for locating adisturbance in a power system based upon disturbance power and energy.

2. Related Art

The construction and operation of power systems has been generally knownfor years. However, with the relatively recent proliferation ofsensitive electronic loads such as ASDs and microprocessors, the subjectof power quality has recently received much interest. Efforts have beenplaced over the previous several years in an effort to characterize theoverall level of power quality delivered to customers on variouselectric systems, Much work has also been done to develop systems thatautomatically identify the major types of power quality disturbancesmeasured on distribution networks, such as capacitor switching, voltagesag, and impulsive transients.

Various types of commercial loads, such as semiconductor processingplants, have enhanced requirements for clean, continuous power. When thepower is interrupted for any reason, the work within the plants may alsobe interrupted, oftentimes causing damage to ongoing processes. Thus,utility companies are often held to an agreed upon level of performancewith respect to such loads. If a disturbance occurs, the utility companymay recompense the customer for damages caused. Further, in the nearfuture, parties responsible for disturbances may be penalized forcausing interruptions in the power supply that result in customerdowntime. However, presently, disturbances cannot be easily located.Resultantly, liability relating to caused disturbances is difficult toassign.

Thus, there is a need in the art for locating disturbances within powersystems in a reliable manner so that liability for causing thedisturbances may be assigned.

SUMMARY OF THE INVENTION

Thus, in order to overcome the shortcomings of the prior systems, amongother shortcomings, a disturbance locating system constructed accordingto the present invention is deployed within a power grid to estimate arelative direction to a disturbance in a power system. The systemincludes a voltage transducer, a current transducer and disturbanceenergy determination circuitry. The system may also include disturbancepower determination circuitry.

The voltage transducer couples to an output of a voltage transformer,the output of the voltage transformer representative of a voltage on aline within the power grid. The current transducer couples to an outputof a current transformer, the output of the current transformerrepresentative of the current flowing through the line, the outputhaving a forward reference direction and a behind reference direction.According to one embodiment, the voltage and current transformers arehard wired to the line. However, in another embodiment, the voltage andcurrent transformers need not require physical coupling to the line toproduce outputs representative of the state of the line.

The disturbance energy determination circuitry couples to the voltagetransducer and the current transducer. Based upon the inputs received,the disturbance energy determination circuitry determines disturbanceenergy flowing in the line and estimates a relative direction to asource of the disturbance as either in front of or behind of thedisturbance locating system. The disturbance energy determinationcircuitry may include disturbance power determination circuitry thatcouples to the voltage transducer and the current transducer. In suchcase, the disturbance power is provided to the disturbance energydetermination circuitry for estimating the relative direction to thedisturbance.

A method for determining a relative direction to a source of adisturbance according to the present invention may be performed inconjunction with the disturbance locating system. The method includes asa first step monitoring a current flowing through, and a voltage on theline in the power grid at the location. Next, the method includesdetermining a steady state power flow through the line and a transientpower flow through the line during a disturbance condition. Based uponthe steady state power flow and the transient power flow through theline, the method includes determining a disturbance power flow throughthe line. Then, based upon the disturbance power flow through the line,method includes determining a relative direction to the source of thedisturbance. The method may also include determining a disturbanceenergy flow through the line and determining the relative direction tothe source of the disturbance is also based upon the disturbance energyflow through the line.

Moreover, other aspects of the present invention will become apparentwith further reference to the drawings and specification which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a power grid in which disturbancelocating systems constructed according to the present invention arestrategically placed to determine the location of disturbances withinthe power grid;

FIG. 2 is a block diagram illustrating the components of a disturbancelocating system constructed according to the present invention;

FIG. 3 is a circuit diagram illustrating a circuit used for simulatingoperating conditions of a power grid during closing of a capacitor bank,the simulated operating conditions employed to demonstrate the principleof operation of a disturbance locating system constructed according tothe present invention;

FIGS. 4 and 5 are signal diagrams illustrating simulated current andvoltage produced during the simulated disturbance of the circuit of FIG.3;

FIGS. 6 and 7 are signal diagrams illustrating the simulated power andenergy produced during the disturbance caused by closing the capacitorbank of the circuit of FIG. 3

FIG. 8 is a circuit diagram illustrating locations of disturbancelocating systems within a simulated circuit, such locations chosen sothat the position of a disturbance within the simulated circuit may beidentified;

FIGS. 9 and 10 are signal diagrams illustrating the voltage waveformsfor a faulted phase of the simulated circuit of FIG. 8 at Meters 1 and 2of FIG. 8, respectively;

FIGS. 11 and 12 are signal diagrams illustrating the disturbance energyflow through Meters 1 and 2 of the simulated circuit of FIG. 8,respectively;

FIGS. 13 and 14 are signal diagrams illustrating the disturbance powerthrough Meters 1 and 2 of the simulated circuit of FIG. 8, respectively;

FIGS. 15 and 16 are signal diagrams illustrating one phase of therecorded voltages at Meters 1 and 2 of the simulated circuit of FIG. 8,respectively, during a switching on of a three-phase, 300 kVAr powerfactor-correction capacitor bank at Load B of the simulated circuit ofFIG. 8;

FIGS. 17 and 18 are signal diagrams illustrating the disturbance energyflow through Meters 1 and 2 of the simulated circuit of FIG. 8,respectively, during the switching on of a three-phase, 300 kVAr powerfactor-correction capacitor bank at Load B of the simulated circuit ofFIG. 8;

FIGS. 19 and 20 are signal diagrams illustrating the disturbance powerthrough Meters 1 and 2 of the simulated circuit of FIG. 8, respectively,during the switching on of a three-phase, 300 kVAr powerfactor-correction capacitor bank at Load B of the simulated circuit ofFIG. 8;

FIGS. 21, 22 and 23 are signal diagrams illustrating the phase A voltageand current, the disturbance energy through a meter and the disturbancepower, respectively, for an actual sag disturbance recorded on TUElectric transmission system near Austin, Tex.;

FIGS. 24, 25 and 26 are signal diagrams illustrating a phase voltage andcurrent, the disturbance energy through a meter and the disturbancepower, respectively, of a capacitor switching event recorded on adistribution feeder in the TU Electric system in Dallas, Tex.;

FIGS. 27, 28 and 29 are signal diagrams illustrating a phase voltage andcurrent, the disturbance energy through a meter and the disturbancepower, respectively, for a capacitor switching event recorded on a TUElectric distribution feeder in Round Rock, Tex.;

FIGS. 30, 31 and 32 are signal diagrams illustrating the phase A voltageand current, the disturbance energy through a meter and the disturbancepower, respectively, for a forward capacitor switching event; and

FIG. 33 is a flow diagram illustrating operation of a disturbancelocating system constructed according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Overview

For two common disturbance types (capacitor switching and voltage sag)and other types of disturbances, it is possible to determine whether adisturbance originates either in front of or behind a disturbancelocating system. This information may tell an engineer whether thedisturbance originated towards, or away from, a substation, orinside/outside a customer facility, depending on the location of thedisturbance locating system. If enough disturbance locating systems areavailable, this information can also be used to pinpoint the source ofthe disturbance, or at least to identify the feeder segment on which itoriginated.

Since nonlinear loads can be thought of as sources of power at harmonicfrequencies, they can be located by noting that harmonic active powertends to flow away from such a load. On the other hand, when a transientdisturbance event is present in a system, it can be thought of as anenergy sink. For example, in the case of a capacitor switchingdisturbance, where a bank of discharged capacitors is switched on-line,energy must be supplied to the bank in order to charge the capacitors.Likewise, during a fault, energy is diverted from other loads to thefault path. The direction of energy flow through the network, therefore,is a key indicator of the disturbance source location.

The direction of the energy flow may be determined by examining sampledthree-phase voltage and current waveforms provided by disturbancelocating systems. Using the recorded voltage and current waveforms, thethree-phase instantaneous power in the circuit is calculated. Duringsteady-state operation, this power has a reasonably constant value.However, when a disturbance event occurs, the network temporarily fallsout of steady-state operation, causing a change in the instantaneouspower flow. Any change in the instantaneous power during the disturbanceis a result of, either directly or indirectly, the disturbance itself.

The difference in the steady-state three-phase instantaneous power andthe three-phase instantaneous power during the disturbance is defined asa “disturbance power”. Changes in the disturbance power and itsintegral, the “disturbance energy,” allow us to make a decision aboutthe location of the disturbance, as the energy tends to flow towards thedisturbance source. The next section uses a simple example circuit toillustrate the procedure.

Deployment and General Construction

FIG. 1 illustrates a power of a power grid 100 in which disturbancelocating systems 102A, 102B, 102C, 102D, 102E and 102F constructedaccording to the present invention are deployed. The power gird is fedby a transmission line 104 that terminates at substation 106. Equipmentwithin the substation 106 transforms the voltage of the electricityflowing in on the transmission line to a distribution voltage level.Distribution lines 108A, 108B and 108C serve loads within the power grid100 at one or more distribution voltage levels. Is shown, distributionline 108A serves residential load consisting of homes 110A, 110B and110C. Further, distribution line 108B serves a hospital 112. Finally,distribution line 108C serves an industrial plant 114.

Within the power grid 100 are capacitor banks 116A, 116B and 116C, eachof which may be switched into service and out of service to compensatefor loading conditions. However, as will be more fully described herein,when these capacitor banks 116A, 116B and 116C switch, they createdisturbances within the system. Contained within the hospital 112 isequipment that must be continuously operational. Thus, the hospital 112includes a back-up generator and battery supply bank to supply acontinuous source of electricity should the power grid 100 fail to servethe hospital's 112 load. Should a disturbance on the system disrupt thesupply of electrical power to the hospital 112, the operator of thepower grid 100 may be liable to the hospital 112.

Industrial plant 114 also may include sensitive electronic equipment.However, the industrial plant 114 also includes non-conforming load,such as motor drives, that places great demands on the power grid 100for short periods of time. Thus, when a disturbance external to theindustrial plant 114 occurs, it may effect the sensitive electronicequipment contained within the industrial plant 114. Further, however,when the non-conforming load within the industrial plant 114 cycles, itmay create disturbances in the power grid 100. Thus, it is useful todetermine whether disturbances are created within the industrial plant114 or external to the industrial plant.

The disturbance locating systems 102A, 102B, 102C, 102D and 102E arestrategically placed throughout the power grid 100 to sensedisturbances. Each of the disturbance locating systems 102A, 102B, 102C,102D and 102E determines whether a disturbance occurred in front of, orbehind of the system. Thus, for example, if a disturbance occurs withinthe industrial plant 114, causing a voltage sag that affects thehospital's 112 load, disturbance locating system 102E determines thatthe disturbance was in front of, and thus within the industrial plant114. To confirm the determination, the other disturbance locatingsystems 102A, 102B, 102C and 102D would determine whether thedisturbance was located in front of, or behind each system.

Further, should a disturbance be caused by the closing of capacitor bank116A, for example, disturbance locating system 102A determines that thedisturbance was in front of it. The result could then be confirmed bydisturbance locating systems 102B and 102D. Moreover, should adisturbance be caused by the closing of capacitor bank 116B, disturbancelocating systems 102B and 102C, in combination, will indicate that thedisturbance was on distribution line 108B, perhaps at capacitor bank116B. Investigation of waveforms recorded by the disturbance locatingsystems 102B and 102C may indicate that the disturbance was of the typecaused by the closing of the capacitor bank 116B. Finally, should alightning strike occur on distribution line 108C, thus creating a shortcircuit, disturbance locating systems 102D and 102E will indicate thatthe disturbance occurred on distribution line 108C. Investigation of therecorded waveforms may then indicate that the disturbance was faultbased.

FIG. 2 illustrates a disturbance locating system 200 constructedaccording to the present invention. The disturbance locating system 200as illustrated may be constructed to include various modular components.These components may form part of a larger device such as a recordingsystem that performs other functions in addition to locatingdisturbances. Components in addition to those required to accomplish theteachings of the present invention will be described only to expand uponthe teachings of the present invention.

The disturbance locating system 200 includes a user interface 202, aprocessor 204, random access memory (RAM) 206, a bus interface 208, diskstorage 210, read only memory 212, a voltage and current interface card218 and communication cards 220 and 222. The user interface 202,processor 204, RAM 206, bus interface 208, disk storage 210 and ROM 212couple to one another via processor bus 214. The processor 204 performsthe processing functions required by the system 200. The processor 204may include a microprocessor programmed specifically for the system 200or may include a custom processor designed and built to performoperations consistent with the present invention. The RAM 206 servicesthe non-permanent storage needs of the system 200 while the ROM 212stores program instructions that are written and require permanentstorage during a power down state. The disk storage 210 provides bulkstorage capability. Further, the bus interface 208 couples a peripheralbus 216 to the processor bus 214 so that the devices coupled to theprocessor bus 214 may communicate with the cards 218, 220 and 222coupled to the peripheral bus 216.

The user interface 202 interfaces the system 200 to a monitor, keyboardand mouse, for example. Such devices allow a user to program and operatethe system 200. However, the system 200 may also be operated remotelyvia one of the communication cards 220 or 222. Communication card 220includes an interface 230 which couples the peripheral bus 216 to aradio 232. The radio couples to an antenna 238 which facilitateswireless communications. Communication card 222 includes an interface234 which couples the peripheral bus 216 to a modem 236 which connectsto a phone line or other wired communication line. Thus, thecommunication card 222 facilitates wired communication with the system200.

The disturbance locating system includes disturbance power determinationcircuitry 205 and disturbance energy determination circuitry 207. In theembodiment illustrated, such circuitry is contained within the processor204 and would be implemented via special programming and/orconstruction. However, in other embodiments, the disturbance powerdetermination circuitry 205 and the disturbance energy determinationcircuitry 207 may be circuitry dedicated to the particular tasks apartfrom the processor 204.

The voltage and current interface card 218 includes an interface 224 aswell as a voltage transducer 226 and a current transducer 228. Thevoltage transducer 226 couples to a voltage transformer or anotherdevice which provides an indication of the voltage on a line beingmonitored by the system. While in some installations, wired leadsconnect the system 200 to the output of an actual voltage transformer,in other installations a wired connection is not required with thevoltage being measured via a non-wired interface. The current transducer226 couples to a current transformer having a directional indication sothat the system 200 knows the direction of current flow with respect tothe system 200. As with the voltage transducer 226, the currenttransducer 228 may also couple directly to the output of a currenttransformer. However, in other installations, the voltage transducer 226may connect to equipment which measures the current flowing in a linewithout a hard-wired current transformer.

Operating Procedure

To illustrate the disturbance power and energy that a disturbancelocating system constructed according to the present invention measures,operation of a simple three-phase RLC switching circuit is examined. Onephase of the circuit is shown in FIG. 3. The following FIGS. 4 and 5illustrate results produced in modeling the three-phase RLC circuitusing a modeling program. The particular modeling program employed iscommonly called the alternate transients program version of EMTP (ATP).In the model, the parameters are chosen as follows: V_(peak)=170 V,R=10Ω, L=10 mH, and C=10 μF. Further, in the model it is assumed thatall three phases of the switch close at the same instant. A two Ωresistor is also placed between each capacitor and ground. The currentsthrough, and voltages across, the capacitors are shown in FIGS. 4 and 5,respectively. The results are as expected.

FIG. 6 shows the three-phase instantaneous power delivered to thecapacitor bank. While the instantaneous power is zero before theswitches close, it has a small non-zero steady-state value. It is clearin this example that the oscillations present in FIG. 6 are caused bythe switching event. The disturbance power is the total instantaneouspower (here, FIG. 6) minus the steady-state instantaneous power (thepart of FIG. 6 after the transient dies out). Therefore, the disturbancepower represents the change in instantaneous power due to thedisturbance. Since the steady-state instantaneous power is small in thiscase, the disturbance power is approximately equal to the instantaneouspower shown in FIG. 6. Taking the integral of the disturbance power overthe duration of the disturbance event gives the disturbance energy,which is the approximate net change in energy flow through the metertowards the disturbance source (here, the capacitor bank). Thedisturbance energy is shown in FIG. 7.

In this example, the final value of the disturbance energy is positive,so the energy flows from left to right (i.e. in the positive direction)through the meter to the capacitor bank. Also note that the polarity ofthe initial peak of the disturbance power also tends to indicate thedirection of the disturbance source. Here, the positive initial peakmatches the positive value of energy flow through the meter. Both ofthese indicators show that the disturbance source is located to theright of the disturbance locating system.

EXAMPLES OF OPERATION

In this section, the procedure described in the Procedure section isapplied to both computer-simulated disturbances and to actualdisturbance waveforms for which the disturbance direction is known.

ATP Voltage Sag Disturbance

A diagram of the network used for the ATP computer simulation, wherelocations of disturbance locating systems (also referred to as arecording device or a Meter) and loads are indicated, is shown in FIG.8. The arrows indicate the direction of positive power flow for eachMeter.

We begin by simulating a single-phase-to-ground fault located betweenMeter 1 and Load A that produces a voltage sag throughout the network.The fault has a duration of one cycle, and a fault impedance of 10Ω. Thevoltage waveforms for the faulted phase at Meters 1 and 2 are shown inFIGS. 9 and 10, respectively. Since Meter 1 shows a greater drop involtage, we can deduce that it is closer to the fault than Meter 2, butthe voltage waveforms alone provide no further information about thelocation of the fault. The disturbance energy flow through Meters 1 and2, found by taking the integral of the disturbance power, is shown inFIGS. 11 and 12, respectively.

The disturbance energy flow through Meter 1 (FIG. 11) indicates that thefault is located in front of it, while the negative flow shown in FIG.12 indicates that the disturbance is located behind Meter 2. While notshown here, the disturbance energy flowing through the other meters alsoindicates the correct directions. By concurrently examining thedirections given by all of the disturbance locating systems, we canaccurately pinpoint the location of the fault as being in the linesegment in front of Meter 1.

The disturbance power through Meters 1 and 2, shown in FIGS. 13 and 14,respectively, confirms the decision made above. In each case, thepolarity of the initial peak is the same as the polarity of the finalvalue of the disturbance energy. Hence, we are able to make a decisionabout the disturbance source locations with a relatively high degree ofconfidence.

Similar results are also obtained for high and low impedance faults (50Ωand 3Ω, respectively), as well as for balanced three-phase-to-groundfaults.

ATP Capacitor Switching Disturbance

Next, we placed a three-phase, 300 kVAr power factor-correctioncapacitor bank at Load B of FIG. 8. Unlike the three-phase capacitorswitching example described above, where the three switches were closedat the same instant, each of the switches here flashes over near thepeak of the associated phase voltage. One phase of the recorded voltagesat Meters 1 and 2 is shown in FIGS. 15 and 16, respectively.

Although FIGS. 15 and 16 look nearly identical, the disturbance sourceis located behind Meter 1, and in front of Meter 2. FIGS. 17 and 18 showthe disturbance energy flow through Meters 1 and 2, respectively, wherewe see inconsistent results. Although there is a great deal moredisturbance energy flow through Meter 2 than through Meter 1, thedisturbance energy is positive in both cases, even though thedisturbance is not located in front of both meters. If the energy flowsfrom both meters are available, then it is clear by examining therelative magnitude that the disturbance source is more likely located infront of Meter 2. However, if, for example, only Meter 1 were present,finding the direction from the disturbance energy alone would yieldincorrect results. It is interesting to note that the final value ofenergy delivered to the capacitor bank, shown in FIG. 18, isapproximately equal to the stored energy in the capacitors given by 3*½CV_(peak) ².

To overcome this inconsistency, we propose that the initial peak of thedisturbance power be used, along with the energy flow, to ensure thatthe direction of the disturbance is determined correctly. FIGS. 19 and20 show the disturbance power oscillations for Meters 1 and 2,respectively. From FIG. 19, we can see that the initial peak isnegative, while FIG. 20 shows that the initial peak is positive. Thepositive initial peak and relatively high positive energy flow for Meter2 provide strong evidence that the disturbance source is located infront of Meter 2. On the other hand, the relatively low energy flowthrough Meter 1, coupled with the negative initial peak, indicate thatit is not likely that the disturbance source is located in front ofMeter 1. Therefore, by examining both pieces of evidence, we are stillable to make an accurate decision about the disturbance sourcedirection. Similar results are also obtained from the other meterspresent in the circuit, and for a separate case with the capacitorsinstalled at Load C.

Recorded Voltage Sag

FIG. 21 shows the phase A voltage and current for an actual sagdisturbance recorded on Texas Utilities Electric's (TU Electric's)transmission system near Austin, Tex. Before the disturbance event, thecurrent slightly lags the voltage. When the fault is on, however, thecurrent leads the voltage, indicating a fault in the negative direction,or behind the disturbance locating system. FIG. 22 shows the disturbanceenergy through the meter. When the fault clears at approximately 0.4seconds, the negative value of disturbance energy indicates a fault inthe negative direction (i.e., behind the meter), confirming the resultsgiven by the phase angle observation. The net energy starts to riseagain as the system recovers from the fault, but this is not a concern,as it occurs only after the fault has cleared and the system has reacheda new steady-state.

The disturbance power for this sag disturbance is shown in FIG. 23. Asbefore, the negative initial peak confirms the decision we made based onthe disturbance energy, and allows us to identify the source locationwith a greater degree of confidence.

Recorded Capacitor Switching

FIG. 24 shows the voltage for one phase of a capacitor switching eventrecorded on a distribution feeder in the TU Electric system in Dallas,Tex. The disturbance shown in the figure is known to have been caused bya capacitor switching event that took place behind the meter. Theassociated disturbance energy, shown in FIG. 25, oscillates about zerountil the disturbance is nearly over (about 0.030 sec), at which time itbegins to climb due to the circuit entering a new steady-state.Therefore, at the effective end of the disturbance, the disturbanceenergy is “small”, and the test is inconclusive. We recommend that“small” be defined as less than 80% of the maximum excursion of thewaveform (i.e. 0.80*2200 J in this case).

In a case such as this one where the disturbance energy test isinconclusive, we may still be able to determine the direction based onthe disturbance power. By looking at the disturbance power in FIG. 26,we see that the initial peak is negative, which indicates that thedisturbance originates in the negative direction. Thus, even though weare not able to make a conclusion based on the energy flow, we are stillable to find the correct direction by examining the initial peak of thedisturbance power.

FIG. 27 shows one phase voltage for a capacitor switching event recordedon a TU Electric distribution feeder in Round Rock, Tex. The source ofthis disturbance is known to have been located in front of the meter.FIG. 28 shows the associated disturbance energy, while FIG. 29 shows thedisturbance power. As we see in FIGS. 28 and 29, both indicators (i.e.,disturbance energy and the initial peak of the disturbance power) are inagreement.

The results for another forward capacitor switching e(vent are shown inFIGS. 30, 31, and 32. For this disturbance, the net disturbance energyis positive, while the initial peak of the disturbance power isnegative. In this case, where there is a strong positive energy flow, wedecide that the disturbance must be in front of the meter (as itactually was). The decision, however, is not confirmed by the initialpeak of the disturbance power. Therefore, our confidence in the decisionis not as high as for the event shown in FIG. 27, where both indicatorsgive the same result.

Method of Operation

Consistent with the above descriptions, a disturbance locating systemconstructed according to the present invention makes a judgment as towhich side of the disturbance locating system a power qualitydisturbance event originates by examining sampled voltage and currentwaveforms. This is accomplished by examining the disturbance power andenergy flow and the polarity of the initial peak of the disturbancepower. If enough disturbance locating systems are available in anetwork, the source of the disturbance may be pinpointed with a highdegree of accuracy.

FIG. 33 sets out the steps of a method of operation according to thepresent invention. Operation commences at step 3302 wherein the systemcontinually records the voltage on the line and current flowing throughthe line at a location of observation on the line. After a disturbancehas been detected, the method determines the beginning and end points ofthe disturbance event. Then, at step 3304, the method includescalculating the three-phase instantaneous power (IP) before, during, andafter the event, using the equation:

IP=V _(a) I _(a) +V _(b) I _(b) +V _(c) I _(c)  (Equation 1)

Once the three-phase instantaneous power has been calculated before,during and after the event, the method includes determining the steadystate power P_(ss), and the transient disturbance power P_(TRANS). Usingthese values, the method then includes determining the disturbance powerwhich is the difference between the three-phase instantaneous power andthe steady state power P_(ss). The disturbance power is then integratedat step 3308 to determine the disturbance energy.

Next, at step 3312, the method includes determining whether the finaldisturbance energy, DE_(FIN) is greater than or equal to eighty percent(80%) of the peak excursion, DE_(PE) of the disturbance energy. If thefinal value of the disturbance energy is greater than or equal to 80% ofthe peak excursion of the disturbance energy during the event, operationproceeds to step 3314 and the energy test is conclusive. The disturbancedirection is the same as the polarity of the final disturbance energyvalue. If the polarity of the initial peak of the disturbance powermatches the polarity of the final disturbance energy value, then we havea high degree of confidence. Else, we still declare the disturbance tobe in the direction indicated, by the disturbance energy, but with alesser degree of confidence.

If the final value of the disturbance energy is less than 80% of thepeak excursion of the disturbance energy at step 3312, operationproceeds to step 3316 where it is determined that the energy test isinconclusive. In such case, the disturbance direction is determined byexamining the polarity of the initial peak of the disturbance power.From both steps 3314 and 3316, the method concludes.

While only two major types of disturbances are described herein, themethod and system presented are applicable to other disturbance types,as well. For example, motor starting disturbances that induce voltagesags are prime candidates, since a great deal of energy must bedelivered to the motor to bring it up to speed. This information mayprove valuable to utilities interested in locating the sources ofrecorded disturbances in order to determine whether a disturbanceoriginated inside or outside of a customer facility, for example.

In view of the above detailed description of the present invention andassociated drawings, other modifications and variations will now becomeapparent to those skilled in the art. It should also be apparent thatsuch other modifications and variations may be effected withoutdeparting from the spirit and scope of the present invention as setforth in the claims which follow.

What we claim is:
 1. For use in estimating the direction to adisturbance source in a power system, an apparatus comprising: a voltagetransducer coupleable to the power system and operative to produce afirst signal representative of a voltage within the power system; acurrent transducer coupleable to the power system and operative toproduce a second signal representative of a current within the powersystem; and a logic circuit coupled to the voltage transducer and thecurrent transducer, the logic circuit being operative to calculate adisturbance quantity based upon the first and second signals, the logiccircuit using the disturbance quantity to estimate the direction to thedisturbance source, wherein the logic circuit further comprises: acomputer readable storage medium operative to store a program, theprogram comprising an instruction code; and a processor operativelycoupled to the storage medium and operative to perform a processingfunction based upon the instruction code, wherein the storage mediumcomprises a read only memory.
 2. For use in estimating the direction toa disturbance source in a power system, an apparatus comprising: avoltage transducer coupleable to the power system and operative toproduce a first signal representative of a voltage within the powersystem; a current transducer coupleable to the power system andoperative to produce a second signal representative of a current withinthe power system; and a logic circuit coupled to the voltage transducerand the current transducer, the logic circuit being operative tocalculate a disturbance quantity based upon the first and secondsignals, the logic circuit using the disturbance quantity to estimatethe direction to the disturbance source, wherein the logic circuitfurther comprises: a computer readable storage medium operative to storea program, the program comprising an instruction code; and a processoroperatively coupled to the storage medium and operative to perform aprocessing function based upon the instruction code, wherein the storagemedium comprises a disk drive.
 3. For use in estimating the direction toa disturbance source in a power system, an apparatus comprising: avoltage transducer coupleable to the power system and operative toproduce a first signal representative of a voltage within the powersystem; a current transducer coupleable to the power system andoperative to produce a second signal representative of a current withinthe power system; and a logic circuit coupled to the voltage transducerand the current transducer, the logic circuit being operative tocalculate a disturbance quantity based upon the first and secondsignals, the logic circuit using the disturbance quantity to estimatethe direction to the disturbance source, wherein the logic circuitfurther comprises: a computer readable storage medium operative to storea program, the program comprising an instruction code; and a processoroperatively coupled to the storage medium and operative to perform aprocessing function based upon the instruction code, wherein the storagemedium comprises a random access memory.
 4. For use in estimating thedirection to a disturbance source in a power system, an apparatuscomprising: a voltage transducer coupleable to the power system andoperative to produce a first signal representative of a voltage withinthe power system; a current transducer coupleable to the power systemand operative to produce a second signal representative of a currentwithin the power system; and a logic circuit coupled to the voltagetransducer and the current transducer, the logic circuit being operativeto calculate a disturbance quantity based upon the first and secondsignals, the logic circuit using the disturbance quantity to estimatethe direction to the disturbance source, wherein the logic circuitcomprises dedicated circuitry.
 5. For use in estimating the direction toa disturbance source in a power system, an apparatus comprising: avoltage transducer coupleable to the power system and operative toproduce a first signal representative of a voltage within the powersystem; a current transducer coupleable to the power system andoperative to produce a second signal representative of a current withinthe power system; a logic circuit coupled to the voltage transducer andthe current transducer, the logic circuit being operative to calculate adisturbance quantity based upon the first and second signals, the logiccircuit using the disturbance quantity to estimate the direction to thedisturbance source; and a communication device operatively coupled tothe logic circuit and coupleable to a communication channel.
 6. Theapparatus of claim 5, wherein the logic circuit is operative to passinformation related to the direction to the disturbance source to thecommunication device, and the communication device is operative toforward the information via the communication channel.
 7. The apparatusof claim 5, wherein the communication device comprises a radiotransmitter and the communication channel comprises a wireless channel.8. The apparatus of claim 5, wherein the communication device comprisesa modem transmitter and the communication channel comprises a wiredcommunication line.
 9. In a power grid a method for estimating arelative direction from a monitoring location on a line to a source of adisturbance, the method comprising: monitoring a current flowing throughthe line in the power grid at the monitoring location; monitoring avoltage on the line in the power grid at the monitoring location,determining a disturbance power flow through the line; and based on thedisturbance power flow through the line, estimating a relative directionto the source, wherein the disturbance power flow is determined from thedifference between a steady state power flow and a power flow during thedisturbance.
 10. In a power grid a method for estimating a relativedirection from a monitoring location on a line to a source of adisturbance, the method comprising: monitoring a current flowing throughthe line in the power grid at the monitoring location; monitoring avoltage on the line in the power grid at the monitoring location,determining a disturbance power flow through the line; and based on thedisturbance power flow through the line, estimating a relative directionto the source, wherein the monitoring of the current is performed usinga current probe coupled to a current transformer.
 11. In a power grid amethod for estimating a relative direction from a monitoring location ona line to a source of a disturbance, the method comprising: monitoring acurrent flowing through the line in the power grid at the monitoringlocation; monitoring a voltage on the line in the power grid at themonitoring location, determining a disturbance power flow through theline; and based on the disturbance power flow through the line,estimating a relative direction to the source, wherein the monitoring ofthe voltage is performed using a voltage probe coupled to a voltagetransformer.
 12. In a power grid a method for determining a relativedirection from a monitoring location on a line to a source of adisturbance, the method comprising: monitoring a current flowing throughthe line in the power grid at the monitoring location; monitoring avoltage on the line in the power grid at the monitoring location,determining a disturbance energy flow through the line; and based on thedisturbance energy flow through the line, estimating a relativedirection to the source of the disturbance from the monitoring location,wherein the disturbance energy flow is determined from the differencebetween a steady state energy flow and an energy flow during thedisturbance.
 13. In a power grid a method for determining a relativedirection from a monitoring location on a line to a source of adisturbance, the method comprising: monitoring a current flowing throughthe line in the power grid at the monitoring location; monitoring avoltage on the line in the power grid at the monitoring location,determining a disturbance energy flow through the line; and based on thedisturbance energy flow through the line, estimating a relativedirection to the source of the disturbance from the monitoring location,wherein the final value of the disturbance energy is compared to thepeak excursion of the disturbance energy.
 14. In a power grid a methodfor determining a relative direction from a monitoring location on aline to a source of a disturbance, the method comprising: monitoring acurrent flowing through the line in the power grid at the monitoringlocation; monitoring a voltage on the line in the power grid at themonitoring location, determining a disturbance energy flow through theline; and based on the disturbance energy flow through the line,estimating a relative direction to the source of the disturbance fromthe monitoring location, wherein the estimate of the relative directionto the source of the disturbance from the monitoring location is basedupon the polarity of the final value of the disturbance energy.
 15. In apower grid a method for determining a relative direction from amonitoring location on a line to a source of a disturbance, the methodcomprising: monitoring a current flowing through the line in the powergrid at the monitoring location; monitoring a voltage on the line in thepower grid at the monitoring location, determining a disturbance energyflow through the line; based on the disturbance energy flow through theline, estimating a relative direction to the source of the disturbancefrom the monitoring location; and determining the disturbance power flowin the line based on the disturbance energy flow through the line;wherein the estimating of the relative direction to the source of thedisturbance from the monitoring location is also based upon thedisturbance power flow in the line.
 16. A disturbance locating systemused to estimate the location of a disturbance source in a power system,the disturbance locating system comprising: a plurality of apparatusesto estimate the direction to the location of the disturbance source,each apparatus located at a measurement position, at least one of theapparatuses comprising: (i) a voltage transducer which is coupleable tothe power system and produces a signal representative of a voltage inthe power system, (ii) a current transducer which is coupleable to thepower system and produces a signal representative of a current flowingwithin the power system, the signal having a forward reference directionand a behind reference direction corresponding to the current flow,(iii) disturbance energy determination circuitry coupled to the voltagetransducer and the current transducer, the circuitry determining ameasure of disturbance energy and estimating a direction of disturbanceenergy flow with respect to the system as either in front of or behindthe disturbance locating apparatus, and (iv) a transmitter devicecoupleable to a communication channel and operative to transmitinformation related to the direction of the disturbance source; and asystem level processing circuit operative to collect information relatedto the direction of the disturbance source from the plurality ofapparatuses and to use the collected information to refine the estimateof the location of the disturbance source.
 17. The disturbance locatingsystem of claim 16, wherein the system level processing circuit furthercomprises a processor for interpreting the approximate location of adisturbance in a power system from said direction information.
 18. Thedisturbance locating system of claim 16, wherein the transmittercomprises a modem coupleable to a phone line.
 19. The disturbancelocating system of claim 17, wherein the transmitter comprises a modemcoupleable to a wired communication line.
 20. The disturbance locatingsystem of claim 16, wherein the transmitter comprises a radio coupled toan antenna for wireless communications.
 21. The disturbance locatingsystem of claim 16, wherein the system level processing circuit is asecond one of the apparatuses.
 22. The disturbance locating system ofclaim 16, wherein at least one of the apparatuses further comprises: acomputer readable storage medium operative to store a program, theprogram comprising an instruction code; and a processor operativelycoupled to the storage medium and operative to perform a processingfunction based upon the instruction code.
 23. The disturbance locatingsystem of claim 16, wherein at least one of the apparatuses furthercomprises dedicated circuitry.
 24. A disturbance locating system used toestimate the location of a disturbance source in a power system, thedisturbance locating system comprising: a plurality of apparatuses toestimate the direction to the location of the disturbance source, eachapparatus located at a measurement position, at least one of theapparatuses comprising: (i) a voltage transducer which is coupleable tothe power system and produces a signal representative of a voltage inthe power system, (ii) a current transducer which is coupleable to thepower system and produces a signal representative of a current flowingwithin the power system, the signal having a forward reference directionand a behind reference direction corresponding to the current flow,(iii) disturbance power determination circuitry coupled to the voltagetransducer and the current transducer, the circuitry determining ameasure of disturbance power and estimating a direction of disturbancepower flow with respect to the system as either in front of or behindthe disturbance locating apparatus, and (iv) a transmitter devicecoupleable to a communication channel and operative to transmitinformation related to the direction of the disturbance source; and asystem level processing circuit operative to collect information relatedto the direction of the disturbance source from the one or moreapparatuses and to use the collected information to refine the estimateof the location of the disturbance source.
 25. The disturbance locatingsystem of claim 24, wherein the system level processing circuit furthercomprises a processor for interpreting the approximate location of adisturbance in a power system from the direction information.
 26. Thedisturbance locating system of claim 24, wherein the transmittercomprises a modem coupleable to a phone line.
 27. The disturbancelocating system of claim 24, wherein the transmitter comprises a modemcoupleable to a wired communication line.
 28. The disturbance locatingsystem of claim 24, wherein the transmitter comprises a radio coupled toan antenna for wireless communications.
 29. The disturbance locatingsystem of claim 24, wherein the system level processing circuit is asecond one of the apparatuses.
 30. The disturbance locating system ofclaim 24, wherein at least one of the apparatuses further comprises: acomputer readable storage medium operative to store a program, theprogram comprising an instruction code; and a processor operativelycoupled to the storage medium and operative to perform a processingfunction based upon the instruction code.
 31. The disturbance locatingsystem of claim 23, wherein at least one of the apparatuses furthercomprises dedicated circuitry.
 32. An apparatus to estimate thedirection to a disturbance source in a power system, the apparatuscomprising: a voltage transducer which is coupleable to the power systemand produces a signal representative of a voltage in the power system; acurrent transducer which is coupleable to the power system and producesa signal representative of a current flowing within the power system,the signal having a forward reference direction and a behind referencedirection corresponding to the current flow; and disturbance energydetermination circuitry coupled to the voltage transducer and thecurrent transducer, the circuitry determining a measure of disturbanceenergy and estimating a direction of disturbance energy flow withrespect to the system as either in front of or behind the disturbancelocating apparatus, wherein the voltage transducer iselectro-magnetically coupled to the power system and wherein the currenttransducer is electro-magnetically coupled to the power system.
 33. Anapparatus to estimate the direction to a disturbance source in a powersystem, the apparatus comprising: a voltage transducer which iscoupleable to the power system and produces a signal representative of avoltage in the power system; a current transducer which is coupleable tothe power system and produces a signal representative of a currentflowing within the power system, the signal having a forward referencedirection and a behind reference direction corresponding to the currentflow; and disturbance energy determination circuitry coupled to thevoltage transducer and the current transducer, the circuitry determininga measure of disturbance energy and estimating a direction ofdisturbance energy flow with respect to the system as either in front ofor behind the disturbance locating apparatus, wherein the voltagetransducer is operative to monitor the voltage via a wireless connectionand wherein the current transducer is operative to monitor the currentvia a wireless connection.
 34. An apparatus to estimate the direction toa disturbance source in a power system, the apparatus comprising: avoltage transducer which is coupleable to the power system and producesa signal representative of a voltage in the power system; a currenttransducer which is coupleable to the power system and produces a signalrepresentative of a current flowing within the power system, the signalhaving a forward reference direction and a behind reference directioncorresponding to the current flow; and disturbance energy determinationcircuitry coupled to the voltage transducer and the current transducer,the circuitry determining a measure of disturbance energy and estimatinga direction of disturbance energy flow with respect to the system aseither in front of or behind the disturbance locating apparatus, whereinthe disturbance energy determination circuitry further comprises astorage apparatus, a memory apparatus, a processor apparatus and acommunication apparatus for determining a measure of disturbance energyand disturbance power and estimating the direction of disturbance energyflow with respect to the system as either in front of or behind thedisturbance locating apparatus.
 35. In a power grid a method fordetermining a relative direction from a monitoring location on a line toa source of a disturbance, the method comprising: monitoring a currentflowing through the line in the power grid at the monitoring location;monitoring a voltage on the line in the power grid at the monitoringlocation, determining a disturbance energy flow through the line; andbased on the disturbance energy flow through the line, estimating arelative direction to the source of the disturbance from the monitoringlocation, wherein the monitoring location is capable of being interfacedby a user and wherein determining the disturbance energy flow throughthe line includes determining an end point and a beginning point of thedisturbance using data stored on a storage apparatus.
 36. The method ofclaim 35, further comprising: calculating a steady state power flowthrough the line using data stored in the storage apparatus; calculatinga transient power flow through the line using data stored in the storageapparatus; and determining the disturbance energy flow through the lineusing a processor, the processor integrating the difference between thetransient power flow through the line and the steady state power flowthrough the line.